The present invention relates to an impurity introduction layer, a junction, and other processed products, and more particularly concerns a forming method of a junction for use in forming an electronic element on a semiconductor substrate to be used in a semiconductor device, a solar battery, or the like, or a plasma doping method and an apparatus thereof for use in introducing an impurity in a junction forming method used for a liquid crystal panel, a solar battery, or the like, and for forming an electronic element on a substrate with a semiconductor thin film formed on its substrate surface.
For example, upon forming an element region on a semiconductor substrate, a large number of pn junctions are used. Moreover, an SOI (Silicon On Insulator) substrate, which has a silicon thin film formed on its substrate surface with an insulating film interposed therebetween, has been widely used in various semiconductor devices such as DRAMs. Furthermore, a glass substrate with a semiconductor thin film formed on its substrate surface has drawn attentions because a small-size and high-speed liquid crystal panel can be obtained by integrating driving circuits for a liquid crystal including thin-film transistors (TFT) into this semiconductor thin film. Further, a semiconductor device having pn junctions formed on a semiconductor substrate or a substrate with a semiconductor thin film formed on its substrate surface has been widely used as a solar battery.
In this manner, upon forming various semiconductor devices, such pn junctions are used. As a method for forming these pn junctions, a method has been conventionally proposed in which after a p-type impurity such as boron has been introduced into an n-type silicon substrate or an n-type silicon thin film by ion implantation, or after an n-type impurity such as phosphorus has been introduced into a p-type silicon substrate or a p-type silicon thin film by ion implantation, an electrically activating process is carried out by a halogen lamp.
As a technique for introducing an impurity onto a surface of a solid-state sample, in addition to the ion implantation method, there has been known a plasma doping method in which an impurity is ionized and introduced into the solid substance with low energy (for example, see U.S. Pat. No. 4,912,065). FIG. 22 illustrates a schematic structure of a plasma doping apparatus for use in a plasma doping method serving as a conventional impurity introducing method, which is described in U.S. Pat. No. 4,912,065. In FIG. 22, a substrate electrode 1, which serves as a base material placing table on which a silicon base material 2 is placed as a base material, is installed in a vacuum container 51. A quartz chamber 52 is installed in the vacuum container 51. While a doping material gas containing a desired element such as B2H6 is being supplied into the vacuum chamber 51 from a gas supply pipe 53, the inside of the vacuum container 51 is evacuated by an exhaust port 54 so that the inside of the vacuum container can be maintained at a predetermined pressure. A microwave is radiated from a microwave guide tube 55 into the vacuum container 51 through the upper portion of the quartz chamber 52.
By an interaction between this microwave and a DC magnetic field formed by an electromagnet 56 located outside the vacuum container 51, a microwave plasma with a magnetic field (electron cyclotron resonance plasma) 57 is formed in the vacuum container 51. A high-frequency power supply 58 is connected to the substrate electrode 1 through a capacitor 25 so that a potential of the substrate electrode 1 can be controlled. The substrate electrode 1 is water-cooled by cooling water that is introduced from a cooling water inlet 59 and discharged from a cooling water outlet 60. Moreover, the DC potential of the substrate electrode 1 is monitored by a voltmeter 61.
In the plasma doping apparatus having this structure, a doping material gas such as B2H6 introduced into the vacuum container 51 is formed into a plasma by a plasma generation means configured by the microwave guide tube 55 and the electromagnet 56, and boron ions in a plasma 57 are introduced into the surface of the base material 2 by the high-frequency power supply 58.
In addition to the above method, as the plasma doping method, there has been proposed a method in which, without using a doping material gas, an impurity source of a solid substance is physically sputtered to obtain a doping material for example, see Japanese Unexamined Patent Publication No. 09-115851 and Japanese Unexamined Patent Publication No. 2004-47695), or a method in which an atmospheric pressure plasma is used (for example, see Japanese Unexamined Patent Publication No. 2005-260139).
As the method for electrically activating introduced ions such as boron ions, in addition to using halogen lamp light, a method for radiating xenon flash lamp light, total solid laser light, or excimer laser light has been well known, and a method using a DC plasma jet has also been proposed (for example, see K. Matsumoto et al., “Activation of B and As in Ultrashallow Junction During Millisecond Annealing Induced by Thermal Plasma Jet Irradiation”, Japanese Journal of Applied Physics 49 (2010) 04DA02). The DC plasma jet has been proposed as being applicable also to crystallization of a silicon thin film (for example, see Japanese Unexamined Patent Publication. No. 2008-53634).
However, the conventional plasma doping methods have an issue of a complicated structure.
In the plasma doping method described in U.S. Pat. No. 4,912,065 exemplified as a conventional art, a hazardous doping material gas that is a special high-pressure gas, for example, B2H6, needs to be used, with the result that an additional facility for gas leakage prevention and detection is required. Moreover, in addition to the doping process, an activating process (using another facility) is required in a separated manner.
Moreover, in the plasma doping methods described in Japanese Unexamined Patent Publication No. 09-115851 and Japanese Unexamined Patent Publication No. 2004-47695 exemplified as conventional arts, although the use of special high-pressure gas can be avoided, an activating process (using another facility) is required in a separated manner in addition to the doping process.
Furthermore, in the plasma doping method described in Japanese Unexamined Patent Publication No. 2005-260139 exemplified as a conventional art, a special high-pressure gas needs to be used. Although no vacuum equipment needs to be used in the doping process, an activating process (using another equipment) is required in a separated manner in addition to the doping process.
It is noted that the DC plasma jet described in K. Matsumoto et al., “Activation of B and As in Ultrashallow Junction During Millisecond Annealing Induced by Thermal Plasma Jet Irradiation”, Japanese Journal of Applied Physics 49 (2010) 04DA02 and Japanese Unexamined Patent Publication No. 2006-53634 each relate to activating and crystallizing processes, of which object is different from that of the present invention.
In view of these issues described above, an object of the present invention is to provide a plasma doping method and an apparatus thereof having a simple structure, and more specifically, a plasma doping method and an apparatus thereof that need not use a hazardous doping material gas and need not carry out an activating process in a separated manner in addition to a doping process.